Electrodeposition of aqueous dispersions of copolymers of polyethylenically unsaturated epoxy-amine adducts

ABSTRACT

Nongelled, amine functional polymers dispersible in water with the aid of a solubilizing acid are provided by copolymerizing (A) an ethylenically unsaturated hydroxy functional amine adduct free of epoxy groups and containing from about 1.4 to about 2.0 ethylenically unsaturated amine groups per molecule, formed from a polyepoxide having a 1,2-epoxy equivalency of from 1.4 to about 2.0 and at least a stoichiometric amount of an ethylenically unsaturated primary amine; and (B) copolymerizable monoethylenically unsaturated monomers, a portion of which is amine-functional. The water solutions are particularly useful to enable corrosion resistant coatings to be electrodeposited at the cathode.

This is a division, of application Ser. No. 576,714, filed 05/12/75.

This invention relates to copolymer of polyethylenically unsaturatedepoxy-amine adducts, to stable aqueous dispersions containing the sameat a pH close to neutral, and to the electrodeposition of such aqueousdispersions at the cathode of a unidirectional electrical system.

In accordance with this invention, amine functional polymers dispersiblein water with the aid of a solubilizing acid are provided bycopolymerizingl (A) an ethylenically unsaturated hydroxy functionalamine adduct free of epoxy groups and containing from about 1.4 to about2.0 ethylenically unsaturated amine groups per molecule, formed from apolyepoxide having a 1,2-epoxy equivalency of from 1.4 to about 2.0 andat least a stoichiometric amount of an ethylenically unsaturated primaryamine; and (B) copolymerizable monoethylenically unsaturated monomers, aportion of which is amine-functional. The stoichiometry is between theamine group and the oxirane group, and the reaction is a simple additionreaction which forms an hydroxy group and a secondary amine group, andall of the epoxy groups are consumed in the addition reaction whichforms the addition reaction product (adduct).

The copolymer is stably dispersible in water at a pH in excess of about5.0, up to about 7.5, and it can be electrodeposited at the cathode,preferably together with an aminoplast curing agent, and cured toprovide cured coatings which have many desirable properties. The highcorrosion resistance is particularly outstanding (salt spray anddetergent resistance), and the high gloss and hardness combined withreasonable flexibility are also impressive.

Referring more particularly to the organic diepoxide which is used,these should have a molecular weight of at least about 350. Sincecommercial epoxy resins are sometimes mixtures of diepoxides andmonoepoxides, these can be used so long as the epoxy functionality is atleast about 1.4. Polyepoxides having an epoxy functionality above about2.0 lead to gelation.

The polyepoxides which are preferred are hydroxy functional polyepoxideshaving a linear aromatic backbone and a molecular weight in the range offrom about 500 to about 6000, preferably 700 to about 4000. Theseinclude a significant hydroxy value (equivalents per 100 grams) of fromabout 0.2 to about 0.4 which participates in the final cure. Thesepolyepoxides are more preferably diglycidyl ethers of bisphenols, suchas bisphenol A, and have a 1,2-epoxy equivalency of 1.4 to 2.0.

From the standpoint of the commercially available materials, the Shellproduct Epon 1001 is preferred, this material having an averagemolecular weight of 1000, a melting point of 67°-74° C., an epoxy valueof 0.20 equivalent per 100 grams, and an hydroxyl value of 0.32equivalent per 100 grams. Other commercial epoxy resins of knowncharacteristics which are also appropriate for use herein are Epon 834,Epon 864, Epon 1004 and Epon 1007.

The ethylenically unsaturated primary amine is subject to widevariation, and has the formula RNH₂. The R group in this formula may beany polymerizable ethylenically unsaturated hydrocarbon, including bothmonoethylenically unsaturated compounds and polyethylenicallyunsaturated compounds. The latter are more commercially available, beingthe amine counterparts of the drying and semi-drying fatty acids, suchas soya fatty acid. The amine counterparts of oleic acid, linoleic acidand linolenic acid will further illustrate the useful polyethylenicmaterials. Allyl carbamate will illustrate the monoethylenic amineswhich are useful. The primary amine based on soya fatty acid isparticularly preferred, being available in commerce with an amine valueslightly in excess of 205, and containing about 98% primary amine. Theunsaturation provided by the soya base provides an iodine value slightlyin excess of 90. The commercial products Kemamine P-997 and KemamineP-997D are particularly preferred (product of Humko Sheffield Chem. Co.)

The reaction between the primary amine and the epoxy groups is itselfconventional, the reactants being cooked together at moderatetemperature (60°-175° C.). An organic solvent may be present tofacilitate reaction, especially inert water-miscible solvents, such asmethyl ethyl ketone. The unsaturation is retained in this reaction toprovide one unsaturated side chain for each epoxy group present in theoriginal diepoxide.

By using an at least approximately stoichiometric proportion ofunsaturated primary amine, all of the epoxy functionality can beconsumed with minimum increase in molecular weight. It is to be observedthat the unsaturation in the amine is inherently inert with respect tothe amino hydrogen atoms. This is because any reactive unsaturationwould be consumed by the amino hydrogen atoms, thus eliminating theunsaturation and the primary nature of the amine. As a result, anyavailable ethylenically unsaturated primary amine is necessarily of thecorrect type and useful herein.

It is to be observed that, in line with conventional terminology asemployed in commerce, functionality not recited in the naming of a classof compounds is not present unless otherwise state. Thus, anethylenically unsaturated primary amine contains these two groups, andnone other.

Excess unsaturated amine may be present, but it represents anunnecessary expense since it simply remains unreacted to be consumed inthe subsequent copolymerization, and tertiary amines having acrylicunsaturation are preferred for incorporation in the copolymer.

The reaction of the diepoxide with the unsaturated primary amineproduces a polyunsaturated hydroxy functional amine which is thencopolymerized, preferably in organic solvent solution, withmonoethylenically unsaturated monomers, preferably including aproportion of amine-functional monomer to produce an amine copolymersolution. The preferred solution copolymerization is itselfconventional, the organic solvent being selected to be water miscible toease the subsequent solubilization in water with the aid of an acid. Anywater-miscible organic solvent may be utilized, such as methyl ethylketone, or 2-ethoxy ethanol, and the like.

Since there is more than one ethylenically unsaturated terminal group,this means that the original polyepoxide is now subject to polymergrowth at more than one location. In preferred practice, we start with adiepoxide, and copolymer formation occurs at both ends of the molecule,and it is this aspect of the situation which enables physical andchemical resistance to be maximized without requiring undue acidity forthe dissolution of the copolymer in water.

The polyunsaturated hydroxy functional amine should constitute from5-75% of the copolymer, preferably from 20-60%. The balance of thecopolymer should consist essentially of copolymerizablemonoethylenically unsaturated monomers, a portion of which is normallyamine-functional to enhance the desired water solubility with the aid ofa solubilizing acid. Such solubility is aided by the presence of from2-20%, preferably from 6-15%, based on the weight of the copolymer, ofmonoethylenically unsaturated amine. The amine may be primary,secondary, or tertiary, and, while monoamines are primarilycontemplated, polyamines, and even hydroxy functional amines, areconsidered to be useful. Tertiary monoamines are particularly preferredto provide greatest solubility in water at highest pH.

As already indicated, the balance of the copolymer consists essentiallyof monoethylenic monomers. Considering first monomers which are notamine-functional, these may be reactive or nonreactive. Any nonreactivemonoethylenic monomer such as styrene, vinyl toluene, methylmethacrylate, ethyl acrylate, dibutyl maleate, acrylonitrile, and thelike is appropriate. The larger the proportion of hydroxy-functionalpolyethylenic unsaturated amine, the less nonreactive monoethylenicmonomer will be used.

The monoethylenically unsaturated monomers used to form the aminecopolymer will preferably include other water soluble reactive monomers,such as acrylamide, N-methylol acrylamide, or hydroxy ethyl acrylate toincrease functional reactivity, especially with aminoplast or phenolformaldehyde curing agents which are desirably incorporated in theaqueous electrocoating bath for electrical codeposit at the cathode withthe amine copolymers of this invention.

Reactive monoethylenic monomers are useful since they increase thereactive functionality, and they may also assist in helping solubilityat the higher pH levels which are desired herein. On this basis,acrylamide, N-methylol acrylamide, hydroxyethyl acrylate, and similarmonomers providing the amide, the N-methylol or the hydroxy group aredesirably present, the total proportion of such reactive monomers beingdesirably in the range of from 5-30%, preferably in the range of 10-25%,based on the total weight of the polymer. The etherified N-methylolgroup is considered to be equivalent to the N-methylol group itselfsince the etherifying alcohol is released on baking.

The class of monoethylenic unsaturated amines is itself well known, thisinvention being illustrated by the commercially available materialdimethyl aminopropyl methacrylate. However, dimethyl aminoethylmethacrylate, monomethyl aminoethyl methacrylate, aminoethylmethacrylate, and the corresponding acrylates, crotonates, and the likeare all fully useful herein. Other amine-functional monomers areillustrated by aminoethyl methacrylate, and t-butyl aminoethylmethacrylate.

Monoethylenically unsaturated tertiary amino amides are also useful inthis invention, and these have the formula: ##STR1## wherein X ishydrogen or methyl, R₁ is C₁ - C₄ alkylidene, and R₂ and R₃ are C₁ - C₄alkyl, preferably both methyl.

These unsaturated amino amides are illustrated by dimethylaminopropylmethacrylamide which has the formula: ##STR2##

The corresponding acrylate is considered to be equivalent and the use ofother alkylidene groups such as the methylidene, ethylidene, andbutylidene groups, does not significantly alter the properties. Whilethe dimethyl amino species is distinctly preferred, the correspondingdiethyl, dipropyl, or dibutyl amino compounds are also useful.

Up to about 30% of the copolymer may be constituted by the aboveunsaturated amino amides, preferably from 5-15%.

It is desired to point out that the monomers which are useful in theproduction of amine copolymers which may be dissolved in water andapplied by electrophoresis at the cathode are themselves well known, andthe above discussion of appropriate monomers will have this in mind.There are two aspects of the situation which are unusual. First, a largeproportion of the copolymer can be constituted by the hydroxy functionalpolyethylenic amine, and this is unusual because the copolymerization ofmonoethylenic monomers with polyethylenic polymers normally results ingelation. The polymers of this invention are nongelled. Second, thecopolymerization which takes place at a plurality of locations in thehydroxy functional polyethylenic amine produces a resin which is bothtough physically, and which is also highly soluble at a pH in the rageof 5.0-7.5.

Copolymerization is carried out in conventional fashion, the monomersbeing preferably dissolved in organic solvent (water miscible solventsare conveniently selected since they are desirably present in the finalwater dispersion) and heat is employed together with a conventional freeradical generating catalyst to cause addition polymerization and theproduction of a linear soluble copolymer.

The copolymers which are dispersed in the electrocoating bath aredesirably obtained and employed in the form of a solution in watermiscible organic solvent, the solvent being desirably present in anamount of at least 10% by weight, based on the weight of the copolymerswhich are dispersed in the water phase. These water miscible solventsare preferably present in an amount not in excess of 150%, based on theweight of the dispersed copolymers. The solvent is most desirablypresent in an amount of from 30-125%, on the same basis. The class ofwater miscible organic solvents useful herein is well known, and theseare illustrated in the accompanying examples.

From the standpoint of water solutions, it will be appreciated that thecopolymers are dispersed in water with the aid of an acid whichsolubilizes the resin, the specific nature of the acid being ofsecondary significance. Inorganic acids such as hydrochloric acid orsulfuric acid are useful, through these do not provide the approximatelyneutral pH and noncorrosive environment which are preferred. It ispresently preferred to employ organic acids such as formic acid, aceticacid, lactic acid or 2-pyridine carboxylic acid. Propionic acid andbutyric acid are also useful. The preferred solubilizing acids can becharacterized as saturated monocarboxylic acids having a dissociationconstant in the range of from about 0.3 to about 5.6.

In the preferred practice of this invention, the final water solution isdesired to have a pH in the range of 5-7.5, more preferably pH 6-7. Whencorrosion resistant equipment is available, lower pH can be tolerated.

Neutralization with acid in this invention is usually 50 to 100% of theamine groups, preferably from 60 to 90%.

It is desired that the aqueous coating compositions of this invention bethermosetting and the thermosetting cure is usually provided by thepresence in the water medium of the coating of dispersed heat-hardeningformaldehyde condensate.

The aqueous compositions of this invention containing the dispersedhydroxy functional acidic resin thus has incorporated therein from5-40%, preferably 10-30%, based on the total weight of resin, of aheat-hardening formaldehyde condensate, which can be dispersed in theaqueous medium. The class of heat-hardening formaldehyde condensates isa well known class including aminoplast resins and phenolic resins.Typical aminoplast resins, all of which are formaldehyde condensates,are urea-formaldehyde, hexamethoxy methyl melamine and water dispersibletransethers thereof with ethanol or other lower alcohol,benzoguanamine-formaldehyde and the like.

It is also possible to use heat-hardening water soluble or dispersiblephenol-formaldehyde resins (phenolic resins), but since these do notinclude nitrogen atoms they do not have any strong tendency to migratetoward the cathode. To accentuate the desired electrophoretic movement,the water dispersible heat-hardening phenolic resin is heat reacted withthe amine copolymer to cause a precondensation to take place, and thetwo resins to become compatibilized with one another. The fact ofreaction is easily observed by the increase in viscosity which takesplace. Thus, phenolic resins are useful herein, but it is usuallypreferred to avoid the needed precondensation, and an advantage of thisinvention is to obtain superior corrosion resistance without relianceupon phenolic resin.

Suitable phenolic resins are illustrated by the well known nongelledalkaline condensates of phenol with excess formaldehyde known as "A"stage resols.

The aqueous electrocoating bath is normally formulated to have a resinsolids content in the range of 2-20%, preferably 5-15%, and theelectrodeposited films are baked to cure the same, baking temperaturesof 250° F. to 600° F. for periods varying from about 20 seconds at thehighest temperature to about an hour at the lowest temperature beingconventional. Preferred bakes are from 350° F. to 475° F. for from about2 to 40 minutes.

Throughout this application, and in the examples and claims whichfollow, all parts are by weight unless otherwise specified.

EXAMPLE 1 Preparation of Diepoxide-Unsaturated Primary Amine Adduct PartA

420 grams of fatty primary amine (Kemamine 997D may be used) containingiodine value of 90 and amine value of 210 were reacted with 1800 gramsof diepoxide having an epoxide value of 900 (Epon 1004 -- Shell may beused).

The reaction was conducted at 90° C. at 80% solids in methyl ethylketone for two hours.

Then methyl ethyl ketone was distilled off at 120° C. and theepoxy-amine adduct dissolved in 2-butoxy ethanol to adjust solids to 70%nonvolatile.

Part B -- Preparation of Epoxy Interpolymer Parts by Weight

300 -- 2-Ethoxy ethanol -- Charge into reactor and heat to 125° C.

151 -- dimethyl aminopropyl methacrylamide

590 -- -Epoxy-amino adduct from Part A (70% solids)

300 -- Styrene

100 -- 2-Ethoxy ethanol

14 -- Cumene-hydroperoxide

7 -- Di-tertiary-butyl peroxide

10 -- Tertiary dodecyl mercaptan.

Premix the above monomers and catalyst and add to the reactor, underconstant agitation at a temperature of 125° C. Add over a 31/2 hourperiod and hold 1 hour. Add 8 parts cumene-hydro peroxide and hold 1hour. Add an additional 8 parts cumene hydro-peroxide and hold for 2hours to complete the reaction.

The final characteristics of the epoxy polymers are:

Solids: -- 59.4%

Viscosity (Gardner)Z₆

Preparation of Electrocoating Composition Parts by Weight

100 -- Epoxy interpolymer of Example 1, Part B

20 -- Methylated-ethylated benzoguanamine resin (XM 1123 - AmericanCyanamid) may be used.

10 -- 2-Ethoxy ethanol

3.1 -- Acetic Acid.

Premix the above, utilizing fast agitation. Then slowly add, withmixing, 700 parts deionized water to provide a colloidal dispersionhaving a solids content of 9.5% and a pH of 6.4.

Electrocoating Operation

The electrocoating operation is performed in a metal tank which isequipped with a magnetic stirrer. The tank serves as an anode and barezinc phosphate treated steel panels are utilized as the cathode. Directcurrent is imposed on the metal container, and on the panels (cathode)from an external circuit. The results which are obtained are as follows:

    ______________________________________                                        Deposition time:    60 seconds                                                Film thickness (mil)                                                                              0.6                                                       Gloss (60°)  89                                                        Cure time           20 minutes                                                Cure temperature    450° F.                                            Pencil hardness     6H                                                        Flexibility (1/4"                                                             conical mandrel)    Pass                                                      Salt spray (5%) 500 hours                                                                         No rusting                                                1% synthetic detergent                                                        solution at 165° F.                                                                        Pass 120 hours.                                           ______________________________________                                    

The invention is defined in the claims which follow.

We claim:
 1. A method of electrodepositing a physically tough, corrosionresistant coating on the cathode of a unidirectional electrical systemfrom an aqueous bath having a pH of 5.0-7.5 comprising passing aunidirectional electrical current through an aqueous electrocoat bathcomprising a water dispersion having a resin solids content of from2-20% by weight, said resin solids including a nongelled,amine-functional polymer dispersed in water with the aid of asolubilizing acid and curing agent therefor, said amine-functionalpolymer being a copolymer of:(A) an ethylenically unsaturated hydroxyfunctional amine adduct free of epoxy groups and containing from about1.4 to about 2.0 ethylenically unsaturated amine groups per molecule,formed from a polyepoxide having a 1,2-epoxy equivalency of from about1.4 to about 2.0 and at least a stoichiometric amount of anethylenically unsaturated primary monoamine; and (B) copolymerizablemonoethylenically unsaturated monomers, a portion of which isamine-functional; and said water dispersion further including anaminoplast or phenol-formaldehyde curing agent for said amine-functionalpolymer.
 2. A method as recited in claim 1 in which said bath has a pHin the range of 6.0 - 7.0.
 3. A method as recited in claim 1 in whichsaid copolymer is solubilized with acetic acid.
 4. A method as recitedin claim 1 in which said copolymer is formed by copolymerization inorganic solvent solution and is dissolved in said bath with said acidand from 10 to 150% of a water miscible organic solvent.
 5. A method asrecited in claim 1 in which said polyepoxide is a polyglycidyl ether ofa bisphenol having a molecular weight of from about 700 to about 4000and said primary monoamine adducted with said polyepoxide is derivedfrom a drying or semi-drying fatty acid.
 6. A method as recited in claim1 in which said unsaturated hydroxy functional amine adduct constitutesfrom 5-75% of the polymer and said copolymer includes from 2-20% ofcopolymerized monoethylenically unsaturated tertiary amine.
 7. A methodas recited in claim 6 in which the tertiary amine functional monomerused is dimethyl aminopropyl methacrylamide.
 8. A method as recited inclaim 6 in which said unsaturated hydroxy functional amine adductconstitutes from 20-60% of the weight of the polymer, and the balance ofthe polymer consists essentially of copolymerized monoethylenicallyunsaturated monomer including from 6-15% of said copolymerizedmonoethylenically unsaturated tertiary amine.